1. Field of the Invention
The present invention generally relates to an electrooptical analyzer, such as an oximeter, for measuring a construction ratio between known components in living tissue, and more particularly to a non-invasive analyzer for optically analyzing living tissue without injuring it.
2. Description of the Prior Art
An optical oximeter for measuring the oxygen saturation of blood, which includes a construction ratio between the hemoglobin oxide (HbO.sub.2) and the hemoglobin (Hb), has been known in the prior art. In such an optical oximeter, the oxygen saturation is determined by measuring the intensity of light transmitted through a living tissue by at least a pair of predetermined wavelengths and by subsequent processing of electrical signals representing the intensities of the pair of wavelengths of light.
The measured intensities of light, however are influenced not only by the absorption of the hemoglobin oxide and hemoglobin, but also by various noise factors. Therefore, it is generally necessary to remove such noise factors to provide a meaningful measurement.
Further, if a measurement is taken with reflected light, the light reflected from the living tissue would also include an additional or multiplying white noise factor due to surface reflection and/or light scattering in the non-blood tissue. Such white noise factors are quite difficult to be satisfactorily avoided or removed. In addition, the measured intensity would also be influenced by the relative movement of the probe to the living tissue.
Generally, in the prior art, the only optical oximeters that have been practical use light transmitted through a limited portion of tissue, e.g., an earlobe or a finger tip attached to an optical probe positioned on the opposite side from a light source.
An example of a prior art oximeter can be found in the Transactions on Biomedical Engineering, Vol. BME-22, No. 3, p. 183, May 1975: "The choroidal eye oximeter: an instrument for measuring oxygen saturation of choroidal blood in vivo.:
Additional prior art references can be found in U.S. Pat. No. 4,086,915, U.S. Pat. No. 3,825,324, U.S. Pat. No. 3,847,483, U.S. Pat. No. 3,787,124, U.S. Pat. No. 3,998,550, and U.S. Pat. No. 4,157,708.
The prior art is still seeking a simplified but accurate oximeter.